1. Field of the Invention
This application relates generally to methods and apparatus for masking as may be used prior to vapor phase diffusion coating of airfoils of gas turbine engine components such as turbine blades.
2. Description of Related Art
Gas turbine engine components such as blades having airfoils often require coatings such as aluminides for environmental protection or as bond coats. Only a portion of the blade, such as the airfoil, that is exposed to the hot gases of the environment requires such protection. A remainder of the blade, such as the root or dovetail of the blade, may not require such protection. Not only does the remainder of the airfoil not require such protection, coating of that portion of the airfoil may be undesirable.
Turbine blades have an airfoil section which extend outward into the hot gases resulting from the combustion of fuel in the combustor portion of the engine. Because of the high temperatures and corrosive effects of such gases on the airfoil section, the standard practice has been to coat the airfoil portions of the turbine blades airfoils with protective coatings that provide insulation from the extremely high temperatures and environmental protection from the corrosive effects of the hot gases. The root or dovetail of the blade is assembled into dovetail slots on the disk or rotor portion of the engine. The walls of the root or dovetail contact the walls of the dovetail slots of the disk or rotor and are subject to fretting which may be exacerbated by coatings applied to the airfoil portion of the turbine airfoil. Thus, in order to achieve the desired properties in the various portions of the turbine blade to maximize the life of the turbine blade, it has been necessary to devise methods to properly coat the airfoil portion of the turbine airfoil without affecting the dovetail portion of the turbine airfoil.
One of the methods of providing the coating to the desired portion of the turbine blade has been to mask the portion of the turbine blade that does not require coating, that is to say, the dovetail, before inserting the turbine airfoil into a coating apparatus. Masking is generally considered to be useful but it is a time-consuming and labor intensive process. Accordingly, less expensive, less time-consuming and less labor intensive masking methods and apparatus for masking are desired. Less material handling is also desirable for improving quality and mask line repeatability.